1. Field of the Invention
The present invention relates to a process for separating a fluid mixture containing three or more components into three or more fractions enriched with the respective components (hereinafter often referred to as "fractions of the respective components" or "enriched fractions of the respective components") and related equipment, and particularly to a process for chromatographic separation of a gaseous or liquid multi-component mixture containing three or more components and equipment for use in carrying out such a process.
2. Prior Art
Wide industrial use has heretofore been made of processes wherein a solid adsorbent is used to chromatographically separate a plurality of components from each other by utilizing a difference therebetween in adsorbability on the adsorbent (hereinafter referred to as "chromatographic separation processes").
Among those processes, so-called "simulated moving bed systems," wherein a number of packed bed units linked with each other in circulatory series are used to effect continuous chromatographic separation, are well known as advantageous processes operable with high productivity. Since these systems are generally employed to fractionate a fluid (gas or liquid) mixture containing tow or more components into two fractions, however, difficulty has been experienced in fractionating a fluid containing three or more components into enriched fractions of the respective components.
In view of the above, some processes have heretofore been proposed for fractionating a fluid containing three or more components into enriched fractions of the respective components, examples of which include a process wherein chromatographic separator equipment of fixed-bed type is used to continuously fractionate a fluid containing three or more components into enriched fractions of the respective components (see Japanese Patent Laid-Open No. 158,105/1988), and a process wherein a liquid feed containing first, second and third components is passed through simulated moving bed equipment wherein bed units packed with a first adsorbent having affinities for the three components decreasing in the order of third component&gt;second component&gt;first component are linked, in alternate continuous series, with bed units packed with a second adsorbent having affinities for the three components decreasing in the order of second component&gt;third component&gt;first component with at least four bed units in total, whereby the liquid feed is fractionated in accordance with the mutually different adsorbabilities of the three components to separate the three components from each other (see Japanese Patent Laid-Open No. 80,409/1989).
However, the above-mentioned processes for fractionating a fluid containing three or more components into three or more fractions of the respective components involve the following problems.
For example, in the former process characterized by comprising the step of circulating a fluid throughout a packed bed without feeding any fresh fluid into the packed bed and without withdrawing the fluid from the packed bed, the circulatory flow rate is identical all across the packed bed because it is fundamentally a fixed-bed type chromatographic separation process. This necessitates an extra length of the packed bed in order to keep the adsorption zone of a component having a weak affinity for an adsorbent from catching up with and outrunning the adsorption zone of a component having a strong affinity for the adsorbent in the course of circulation. This greatly enlarges the size of the equipment and, hence, increases the amount of the adsorbent packed therein as compared with those in the case of simulated moving bed systems. The ensuing problem is that the amount of chromatographic separation treatment (throughput capacity) per unit amount of the adsorbent, which is of great industrial significance in connection with these types of equipment, is decreased. Another problem is that the load of post-treatment to be effected if necessary is increased because the component concentrations of fractions recovered through fractionation are low when produced by this process.
On the other hand, the latter process using the two different adsorbents is advantageous in that fractional separation of three components from each other can achieve excellent results. However, this process is restricted in the variety of fluids, as objects to which the process is applicable, in association with components contained therein, because the process necessitates selection of two different adsorbents having appropriate adsorptive affinities for three separate components.
The present invention has been made in view of the foregoing problems of the conventional processes.
Accordingly, an object of the present invention is to provide a novel process and equipment by which a mixture containing three or more components can be efficiently fractionated into three or more fractions each enriched with a component.
Another object of the present invention is to provide a novel process and equipment by which fractional separation of three or more components from each other can be achieved using only one kind of adsorbent.
Still another object of the present invention is to provide a novel process and equipment by which a mixture containing three or more components can be continuously fractionated into three or more fractions by utilizing a procedure of chromatographic separation on a simulated moving bed.
A further object of the present invention is to provide a novel process and equipment very well suited for a fractionation operation to be carried out particularly on an industrial scale wherein advantage is taken of the chromatographic, simulated moving bed system, thereby minimizing the amount of an adsorbent to be used, which in turn results in smaller equipment and larger throughput capacity per unit amount of the adsorbent.